How much can I lower my 5th wheel hitch?

[North16HighCountryDuramax]

Everything pulls really nice but I find the back of the trailer too low. We camp in hilly campgrounds and my bumper has actually touched. I have read about lowering the back of my 2016 Silverado 2500HD but may be issues with shocks. The hitch in the truck does not adjust up and down but the hitch on the trailer can be adjusted. My question is how much clearance should I keep between the box of the truck and the underside of the fifth wheel part of the trailer?

 

[North16HighCountryDuramax]

I just thought of it now, here are the specs on the trailer:

[vertigo]

Ideally, you should have at the minimum 5-6" from the top of the bed rail to the bottom of the 5th wheel. You want the 5th wheel to be as level as possible.

[Beer Belly]

Nice rig